Dynamical Approach to Microphase Separation in ABCA-Type Tetrablock Copolymers

We study microphase separation of ABCA-type tetrablock copolymers mainly in the weak segregation limit by means of a coarse grained approach. Experiments by Matsushita and his coworkers show that only the non-centrosymmetric (NCS) lamellar structure (with the sequence ...ABCAABCA...) is observed although its local free energy is not markedly different from that of the centrosymmetric (CS) lamellar structure (...ABCAACBA...). To clarify the origin of this unique order, we derive the free-energy functional and the set of kinetic equations for ABCA tetrablock copolymers. By solving this numerically in one dimension, we explore how the NCS lamellar structure is selected.